"Reshoot in progress. After long hours of debate and discussion Ram Gopal Varma (RGV) and I decided to change the look of 'Sarkar 3'. Just kidding," Big B tweeted late on Saturday night.
The actor also shared some photographs from the set, in which he is seen sitting on a bench with an intense look.
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In another, the actor is seen having a conversation with Varma.
Amitabh also tweeted: "You shall be hearing of this pretty soon!"
Presented by Eros International and produced by Allumbra Entertainment, Wave Cinemas and AB Corp, "Sarkar 3" is the third film in Varma's "Sarkar" series.
"Sarkar", which released in 2005, is set in the world of Indian politics. Its sequel "Sarkar Raj" hit the screens in 2008.
"Sarkar 3" will see Amitabh reprising his role as Subhash Nagre. The film will also feature Yami Gautam, Jackie Shroff, Manoj Bajpayee, Amit Sadh, Rohini Hattangadi, Ronit Roy and Bharat Dabholkar.
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Amitabh also stressed the importance of documenting the process of filmmaking for "posterity of the largest film industry in the world".
In a post on his official blog, the "Piku" star said: "It is rare to just sit in an environment of cinema, and talk about cinema and its craft. A documentation that has such immense importance and one that the industry has never done."
"I do hope someday someone shall start this process...not just for their personal self but for the posterity of the largest film industry in the world."